1. Field of the Invention
The present invention relates to an extruded resin film of a thermoplastic resin and a method for producing the same, and particularly to an extruded resin film which exhibits little thermal shrinkage ratio and a method for producing the same.
2. Description of the Related Art
Extruded resin films made of thermoplastic resin have been used in an extremely wide variety of applications, such as interior or exterior of automobiles, exterior of household electric appliances, optical applications including liquid crystal televisions and monitors. In some of such applications, a resin film is subjected to functional coating, such as light-diffusive coating, to be provided with a new function, or a resin film is printed and then the printed film is placed in an injection molding mold to be subjected to injection molding and simultaneous lamination thereof. Therefore, situations have been increasing where a resin film is placed at a temperature equal to or higher than the heat distortion temperature of the thermoplastic resin which constitutes the film, in drying or shaping the film.
However, such an extruded resin film inherently has a large residual strain in its extrusion direction and, as a result, shrinks greatly occur in an environment equal to or higher than the heat distortion temperature. Conversely, an extruded resin film tends to expand in its cross-extruded direction and, therefore, when a film is printed and then dried, or a film is heated for shaping, warped patterns or a warped shape may be produced.
In light of such problems, there have been attempts to control the shrinkage ratio of an extruded resin film. Examples of such attempts include an art of obtaining a low-shrinking acrylic resin film by melt-extruding an acrylic resin through a T die having a slit thickness of 1 mm or less and bringing it into contact with a single metal roll (see, for example, Japanese Patent Kokai Publication No. 2002-3620), and an art of obtaining an acrylic resin sheet having a desired shrinking property by biaxial stretching (see, for example, Japanese Patent Kokai Publication No. Sho 61 (1986)-162319).
However, the film of the former art is observed to expand in the cross-extrusion direction at the heat distortion temperature or higher, which may result in great deformation of patterns printed on the film. As to the film of the latter art, it is necessary to obtain a resin film temporarily and then subject it to biaxial stretching in order to obtain a desired film. This will require a large facility and a large cost.